Low voltage halogen lamps have been a popular replacement for incandescent lamps especially for decorative applications. They are more efficient than traditional incandescent lamps but not as efficient as the modern generation of lighting such as white light emitting diodes (WLEDs) or cold cathode fluorescent lamps (CCFLs). Halogen lamps run very hot and must be placed an appropriate distance away from any combustible materials. They also need a low voltage AC (or DC) supply (i.e., usually between 12 and 24 volts). Traditionally, a low voltage supply for halogen lamps was supplied from the AC source by a step-down transformer. These transformers, since they are designed for 50-60 Hz, must necessarily be made large and heavy. Although they are simple and reliable, they require a large amount of raw materials, especially copper and iron.
With reference to FIG. 1, this figure illustrates a traditional electronic transformer for a halogen lamp. In order to save on raw materials and cost, a common technique has been to replace the 50-60 Hz transformer with what is known as an electronic transformer or e-transformer. The electronic transformer uses a self oscillating resonant circuit to produce an AC signal at 20-40 k Hz. At those higher frequencies a step-down transformer can be made many times smaller than a traditional transformer that runs at 50-60 Hz. The size and overall cost of the electronic transformer is much less than a traditional 50-60 Hz transformer.
The world's desperate need to conserve energy obligates the engineering community to look for low cost methods to retrofit halogen lights using e-transformers with high efficiency alternatives. For example, replacing the halogen lamp should be no more difficult than removing the old halogen bulb and replacing it with a bulb using suitable WLEDs. Due to the realization that halogen lamps are not particularly efficient there has been a trend to replace those halogen lamps with equivalently sized WLED lamps. A 50 W halogen lamp could ideally be replaced by a 10 W (or less) WLED lamp capable of producing the same amount of illumination. The potential power savings is enormous.
However, the problem with the WLED replacement strategy is that the electronic transformers that are used for halogen light fixtures require a minimum load larger than 10 Watts for proper operation. Since most WLED loads are smaller than 10 W these electronic transformers do not operate properly with WLED lamps. Compounding this problem is the situation that in some countries the e-transformer may be placed behind a wall or some locations that are not easily accessible by the consumer. Therefore, this problem will increase the cost of using high efficiency lighting beyond what many consumers would be willing to pay.
Therefore, there is a need for an approach to provide a device or means to allow an electronic transformer to be able to drive highly efficient lamps in a low power level condition, allowing the replacement of old halogen lamps from the existing fixtures with other high efficiency lamps.